From 14dcc01f8f32fd2a2bd8a788a96e68adc491af86 Mon Sep 17 00:00:00 2001
From: fiatjaf <fiatjaf@gmail.com>
Date: Fri, 19 Dec 2025 06:40:22 -0300
Subject: [PATCH] eventstore: SortedMerge() takes a limit and is simpler
 (should be faster) for small limits.

---
 eventstore/combine.go                         | 35 +++++++++++++++++--
 eventstore/combine_test.go                    | 10 +++---
 .../fuzz/FuzzSortedMerge/0076b595fbac65cc     |  7 ++++
 3 files changed, 45 insertions(+), 7 deletions(-)
 create mode 100644 eventstore/testdata/fuzz/FuzzSortedMerge/0076b595fbac65cc

diff --git a/eventstore/combine.go b/eventstore/combine.go
index f10dec9..65ede9a 100644
--- a/eventstore/combine.go
+++ b/eventstore/combine.go
@@ -2,15 +2,46 @@ package eventstore
 
 import (
 	"iter"
+	"slices"
 
 	"fiatjaf.com/nostr"
 )
 
-func SortedMerge(it1, it2 iter.Seq[nostr.Event]) iter.Seq[nostr.Event] {
+// SortedMerge combines two iterators and returns the top limit results aggregated from both.
+// limit is implied to be also the maximum number of items each iterator will return.
+func SortedMerge(it1, it2 iter.Seq[nostr.Event], limit int) iter.Seq[nostr.Event] {
+	if limit < 60 {
+		return func(yield func(nostr.Event) bool) {
+			acc := make([]nostr.Event, 0, limit*2)
+			for evt := range it1 {
+				acc = append(acc, evt)
+			}
+			for evt := range it2 {
+				acc = append(acc, evt)
+			}
+			slices.SortFunc(acc, nostr.CompareEventReverse)
+			for i := range min(limit, len(acc)) {
+				if !yield(acc[i]) {
+					return
+				}
+			}
+		}
+	}
+
 	next1, done1 := iter.Pull(it1)
 	next2, done2 := iter.Pull(it2)
 
-	return func(yield func(nostr.Event) bool) {
+	return func(yieldInner func(nostr.Event) bool) {
+		count := 0
+		yield := func(evt nostr.Event) bool {
+			shouldContinue := yieldInner(evt)
+			count++
+			if count >= limit {
+				return false
+			}
+			return shouldContinue
+		}
+
 		defer done1()
 		defer done2()
 
diff --git a/eventstore/combine_test.go b/eventstore/combine_test.go
index 78f7584..3756434 100644
--- a/eventstore/combine_test.go
+++ b/eventstore/combine_test.go
@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"fiatjaf.com/nostr"
+	"github.com/stretchr/testify/require"
 )
 
 func FuzzSortedMerge(f *testing.F) {
@@ -19,7 +20,7 @@ func FuzzSortedMerge(f *testing.F) {
 		merged := SortedMerge(
 			func(yield func(nostr.Event) bool) {
 				for range len1 {
-					if !yield(nostr.Event{CreatedAt: nostr.Timestamp(start1)}) {
+					if !yield(nostr.Event{ID: nostr.ID(nostr.Generate()), CreatedAt: nostr.Timestamp(start1)}) {
 						return
 					}
 					start1 -= uint(diff1)
@@ -27,19 +28,18 @@ func FuzzSortedMerge(f *testing.F) {
 			},
 			func(yield func(nostr.Event) bool) {
 				for range len2 {
-					if !yield(nostr.Event{CreatedAt: nostr.Timestamp(start2)}) {
+					if !yield(nostr.Event{ID: nostr.ID(nostr.Generate()), CreatedAt: nostr.Timestamp(start2)}) {
 						return
 					}
 					start2 -= uint(diff2)
 				}
 			},
+			int(max(len1, len2)),
 		)
 		result := slices.Collect(merged)
 
 		// assert length
-		if len(result) != int(len1+len2) {
-			t.Fatalf("expected %d events, got %d", len1+len2, len(result))
-		}
+		require.Equal(t, int(max(len1, len2)), len(result), "got a different number of results than expected")
 
 		// assert sorted descending
 		slices.IsSortedFunc(result, func(a, b nostr.Event) int { return -1 * cmp.Compare(a.CreatedAt, b.CreatedAt) })
diff --git a/eventstore/testdata/fuzz/FuzzSortedMerge/0076b595fbac65cc b/eventstore/testdata/fuzz/FuzzSortedMerge/0076b595fbac65cc
new file mode 100644
index 0000000..85e90a9
--- /dev/null
+++ b/eventstore/testdata/fuzz/FuzzSortedMerge/0076b595fbac65cc
@@ -0,0 +1,7 @@
+go test fuzz v1
+uint(52)
+uint(16)
+uint(56)
+uint(7)
+byte('#')
+byte('\x00')